Spinneret for preparing island-in-the-sea yarns

ABSTRACT

Disclosed is a spinneret for preparing island-in-the-sea yarns, wherein island ingredient supply channels are partitioned into a plurality of groups in a discharge portion. The island-in-the-sea yarns prepared using the spinneret can prevent aggregation of island portions in the center thereof, although the number of island portions is 500 or more. Accordingly, island-in-the-sea yarns are considerably advantageous for the preparation of microfibers, since 500 or more island portions can be disposed in one island-in-the-sea yarn and fineness of island portions can thus be reduced. In addition, the island-in-the-sea yarns have an advantage of considerably reduced production costs, since 500 or more microfibers can be produced from one island-in-the-sea yarn. Furthermore, the island-in-the-sea yarns render a specific color according to the ratio of sea portions to island portions and diameter of fibers, without adding chromogenic compounds such as dyes, and are thus applicable to photochromic fibers.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit under 35 U.S.C. §119(a) of KoreanPatent Application Serial No. 10-2009-0012138, filed Feb. 13, 2009,which is incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Technical Field

The present invention relates to a spinneret for preparingisland-in-the-sea yarns, and more specifically, to a spinneret forpreparing island-in-the-sea yarns capable of preventing aggregation ofisland portions during spinning, although the island portions are highin number.

2. Background Art

An island-in-the-sea yarn is a yarn whose cross-section has a structurein which island ingredients are dispersed in a sea ingredient. When thesea ingredient is removed by elution or dissolution duringpost-processing after spinning, only the island ingredient remains.Accordingly, increased preparation costs and environmental problemsdisadvantageously occur due to waste of resins and the use of solvent toelute the sea ingredient. In spite of these problems, island-in-the-seayarns enable preparation of microfibers, which cannot be obtained usingconventional microfiber preparation methods, and are thus widely used asyarns for industrial materials such as artificial suede, filters andcleaning products.

Of conventional island-in-the-sea yarns, the term “sea ingredient”refers to an ingredient eluted or dissolved during post-processing afterspinning, and the term “island ingredient” refers to an ingredient offibers, left behind after removal of the sea ingredient. Processes forpreparing suede fabrics from the island-in-the-sea yarns require aseries of steps including weight-reduction, napping, dying, etc.Fineness uniformity and napping uniformity of micronizedisland-ingredient fibers are considerably important in stabilizingquality of fibers, and arrangement and structure of the cross-sectionsof island-ingredient fibers are thus core factors deciding quality.

Accordingly, in order to maximally utilize the island ingredient,island-in-the-sea yarns are prepared by conjugate-spinning analkali-soluble polymer as a sea ingredient and a fiber-forming polymeras an island ingredient in the form of island-in-the-sea. Theisland-in-the-sea yarns are generally prepared for the purpose ofobtaining microfibers. That is, the prepared island-in-the-sea yarns aretreated with an alkali solution to elute the soluble polymer as the seaingredient and thereby to obtain microfibers comprising only the islandingredient. As such, the method for preparing microfibers from theisland-in-the-sea yarns advantageously exhibits superior spinning anddrawing operation efficiencies and enables preparation of a higherfineness of microfibers, as compared to methods for preparingmicrofibers using direct-spinning, but requires a process forelution-removing the sea ingredient polymer with an organic solventduring post-processing after weaving or knitting. Improvement in qualityof final products can be realized depending on the micronization levelof island-ingredient fibers. Accordingly, a great deal of research anddevelopment are practically conducted to further micronize the finenessof island-ingredient fibers.

In accordance with conventional commercially available technologies todate, the number of island-ingredient fibers obtained is 37 or less andfineness of micronized island-ingredient fibers obtained is 0.05deniers. Accordingly, there is a need to develop methods for preparingisland-ingredient fibers with fineness of 0.04 deniers or less byincreasing the number of island-ingredient fibers to 38 or more.

However, when the number of island-ingredient fibers is 38 or more, thecross-section structure thereof is very important and cross-sectionalarrangement of island-ingredient fibers in island-in-the-sea yarnsshould be elaborately designed. Specifically, FIG. 1 is a top viewillustrating a conventional spinneret for preparing island-in-the-seayarns. More specifically, a spinneret for preparing island-in-the-seayarns 1 includes a discharge portion 2, through which island-in-the-seayarns are discharged, and a peripheral portion 3 surrounding theperiphery of the discharge portion 2. The discharge portion 2 has astructure in which a plurality of island ingredient supply channels 5are radially arranged based on one spinning core 4, and the number ofisland ingredient supply channels 5 may be varied depending on thedesired number of island ingredients. A sea ingredient supply channel 6is formed in the peripheral portion 3 surrounding the periphery of thedischarge portion 2. When an island ingredient and a sea ingredient areinjected through respective supply channels of the spinneret in FIG. 1,the sea ingredient supplied through the sea ingredient supply channel 6in the spinneret is introduced into the discharge portion 2 andsurrounds the island ingredient supply channel 5, while filling thedischarge portion 2. Through this process, island-in-the-sea yarnswherein island portions are arranged in the sea ingredient can beprepared.

FIGS. 2 and 3 show cross-sections of conventional island-in-the-seayarns (comprising 331 island portions) spun through the spinneret ofFIG. 1. In FIG. 2, island portions 12 are concentrically arranged basedon one spinning core 11 in island-in-the-sea yarns and the islandportions take up 30 to 70% of the total cross-section ofisland-in-the-sea yarns. In FIG. 3, island portions 14 are alsoconcentrically arranged based on one spinning core 13 inisland-in-the-sea yarns and the island portions take up 30 to 80% of thetotal cross-section of island-in-the-sea yarns. This cross-sectionalstructure is normal, when island portions are small in number, whileisland portions adjacent to the spinning core 11 formed in the center ofisland-in-the-sea yarns are highly dense and may be aggregated duringspinning, when island portions are large in number (about 300 or higher)or a cross-sectional area ratio of the island portions increases. Thatis, as the number of island portions in island-in-the-sea yarnsincreases, an undesired side-effect (island-conjugation) in which islandportions present in the center of island-in-the-sea yarns are aggregatedand lumped may readily occur. In this regard, application of thearrangement pattern of conventional island-in-the-sea yarns comprising37 or less island portions cannot secure stable formation of fibercross-sections. Accordingly, there is an increasing need for specificdesigns to suitably arrange island portions in the cross-sections ofisland-in-the-sea yarns.

SUMMARY OF THE INVENTION

Therefore, the present invention has been made in view of the aboveproblems, and it is an object of the present invention to provide aspinneret for preparing island-in-the-sea yarns, to prevent aggregationof island portions and obtain chromogenic island-in-the-sea yarns.

In accordance with the present invention, the above and other objectscan be accomplished by the provision of a spinneret for preparingisland-in-the-sea yarns including: a discharge portion, including aplurality of island ingredient supply channels to dischargeisland-in-the-sea yarns; and a peripheral portion arranged in theperiphery of the discharge portion, the peripheral portion including asea ingredient supply channel, wherein the island ingredient supplychannels are partitioned into a plurality of groups in the dischargeportion.

The discharge portion may further include one or more sea ingredientsupply channels.

The island ingredient supply channels may be grouped based on two ormore spinning cores.

The spinning cores may include one standard spinning core arranged inthe center of the island-in-the-sea yarn and a plurality of peripheralspinning cores arranged based on the standard spinning core.

Preferably, distances between the standard spinning core and theperipheral spinning cores may be substantially equivalent.

The peripheral spinning cores may be spaced from one another by auniform distance.

The peripheral spinning cores may be 3 to 20 in number.

The peripheral spinning cores may be 6 to 10 in number.

The number of island portions arranged with respect to one standardspinning core or one peripheral spinning core may be 10 to 300.

The sea ingredient supply channel may be interposed between the standardspinning core and the peripheral spinning core.

The total number of the island ingredient supply channels may be 38 to1,500.

The total number of the island ingredient supply channels may be 500 to1,500.

The total number of the island ingredient supply channels may be 1,000to 1,500.

The island ingredient supply channel groups may have circular, oval,polygonal, or non-circular cross-sections.

The island ingredient supply channel groups may have identical ordifferent shapes.

The spinning cores may be arranged based on the center of the dischargeportion.

A sea ingredient supply channel may be arranged in the center of thedischarge portion.

The spinning cores may be 3 to 20 in number.

The spinning cores may be 6 to 10 in number.

The sea ingredient supply channel may be arranged between the spinningcores.

The discharge portion may have a diameter of 15 to 50 mm.

The island ingredient supply channel may have a diameter of 0.1 to 0.3mm.

The sea ingredient supply channel may have a diameter of 0.1 to 0.3 mm.

The discharge portion may be 2 to 20 in number.

A maximum distance between the centers of adjacent island ingredientsupply channels present in one group may be smaller than a maximumdistance between the centers of adjacent island ingredient supplychannels present in two adjacent groups.

Hereinafter, a brief description will be given of the terms used herein.

Unless specifically mentioned, the term “spinning core” means a specificstandard point at which island ingredient supply channels are grouped(partitioned) on an upper plate of a spinneret.

The term “standard spinning core” means a spinning core acting as acenter and the term “peripheral spinning core” means a remainingspinning core arranged based on the standard spinning core, when thespinning cores are plural in number and are composed of one spinningcore and other spinning cores arranged based on the one spinning core.

The expression “island ingredient supply channels are arranged such thatthey are grouped” means a state in which the island ingredient supplychannels are arranged, based on one spinning core, such that they arepartitioned in a predetermined shape, and for example, when two spinningcores are present in a spinneret, island ingredient supply channels arearranged in a predetermined shape, based on respective spinning coresand the island ingredient supply channels are thus divided into twogroups in the island-in-the-sea yarns spun using the spinneret.

The term “photochromic fiber” means a fiber which does not render colorthrough physical and chemical bonds of color-rendering substances suchas dyes or pigments, but renders color using interference of lightthrough structural and optical design of fibers.

The expression “fibers are birefringent” means that when light isirradiated to fibers having different refractive indices according todirections, the light incident to the fibers is refracted in twodifferent directions.

The term “isotrope” means a property in which an object has a constantrefractive index irrespective of a direction in which light passesthrough the object.

The term “anisotrope” means a property in which optical properties of anobject are varied according to directions of light and an anisotropicobject is birefringent and is the opposite of an isotrope.

The term “optical modulation” means a phenomenon in which irradiatedlight is reflected, refracted, or scattered, or intensity, cycle of wavemotion or characteristics thereof are varied.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and other advantages of thepresent invention will be more clearly understood from the followingdetailed description taken in conjunction with the accompanyingdrawings, in which:

FIG. 1 is a top view illustrating a conventional spinneret for preparingisland-in-the-sea yarns;

FIGS. 2 and 3 are electron micrographs illustrating the cross-section ofisland-in-the-sea yarns prepared using the spinneret of FIG. 1;

FIG. 4 is a top view illustrating a spinneret for preparingisland-in-the-sea yarns according to one embodiment of the presentinvention;

FIG. 5 is a sectional view illustrating group-type island-in-the-seayarns prepared using the spinneret of FIG. 4;

FIG. 6 is a top view illustrating a spinneret for preparingisland-in-the-sea yarns according to another embodiment of the presentinvention;

FIG. 7 is an electron micrograph illustrating group-typeisland-in-the-sea yarns prepared using the spinneret of FIG. 6;

FIG. 8 is a top view illustrating a spinneret for preparingisland-in-the-sea yarns according to another embodiment of the presentinvention;

FIG. 9 is a sectional view illustrating group-type island-in-the-seayarns prepared using the spinneret of FIG. 8; and

FIG. 10 is a sectional view illustrating a passage of light emitted tothe island-in-the-sea yarns prepared using the spinneret according tothe present invention.

DETAILED DESCRIPTION OF THE INVENTION

The island-in-the-sea yarns prepared using the spinneret for preparingisland-in-the-sea yarns of the present invention are free of aggregationof island portions in the center thereof, although the number of islandportions is 500 or more, because the island portions in theisland-in-the-sea yarns are partitioned into two or more groups.Accordingly, island-in-the-sea yarns are considerably advantageous forthe preparation of microfibers, since 500 or more island portions can bedisposed in one island-in-the-sea yarn and fineness of island portionscan thus be reduced. In addition, the island-in-the-sea yarns have anadvantage of considerably reduced production costs, since 500 or moremicrofibers can be produced from one island-in-the-sea yarn.

Furthermore, the island-in-the-sea yarns render a specific coloraccording to the ratio of sea portions to island portions and diameterof fibers, without adding chromogenic compounds such as dyes and arethus applicable to photochromic fibers. The photochromic fibers mayrender a variety of colors according to intensity of light, position andangle of observer.

Furthermore, island-in-the-sea yarns comprising island portions and seaportions exhibiting different optical properties enable formation ofbirefringent interfaces between the island portions and sea portions andcan thus more considerably improve optical modulation efficiency, ascompared to birefringent fibers, and are free of aggregation of islandportions in the center thereof, although the number of island portionsis 500 or more. As a result, the island-in-the-sea yarns maximize anoptical modulation interface area and thus considerably improve opticalmodulation efficiency, as compared to conventional island-in-the-seayarns comprising one spinning core. Accordingly, luminance-enhancedfilms comprising the island-in-the-sea yarns have superior opticalmodulation effects and exhibit considerably improved luminance, ascompared to luminance-enhanced films comprising conventionalbirefringent fibers or island-in-the-sea yarns.

Hereinafter, the present invention will be illustrated in more detail.

The island-in-the-sea yarns prepared using the conventional spinneretfor preparing island-in-the-sea yarns have a cross-sectional structurewherein island portions are concentrically arranged based on onespinning core, or island portions are randomly disposed without aspinning core. This cross-sectional structure is normal, when islandportions are small in number, while island portions adjacent to thespinning core formed in the center of island-in-the-sea yarns are highlydense and may be aggregated during spinning, when island portions arelarge in number (about 300 or higher). That is, as the number of islandportions in island-in-the-sea yarns increases, an undesired side-effect(island-conjugation) in which island portions present in the center ofisland-in-the-sea yarns are aggregated and lumped may readily occur.

Accordingly, in one embodiment, in an attempt to prevent aggregation ofthe island portions, the present invention provides a spinneret forpreparing island-in-the-sea yarns comprising a discharge portioncomprising a plurality of island ingredient supply channels to dischargeisland-in-the-sea yarns, and a peripheral portion, which is arranged inthe periphery of the discharge portion and comprises a sea ingredientsupply channel, wherein the island ingredient supply channels arepartitioned into groups. More preferably, the problem can be solved bydesigning the island ingredient supply channels to be partitioned intogroups based on two or more spinning cores. As a result, the phenomenonin which island portions are excessively concentrated on one spinningcore can be prevented, microfibers can be prepared by forming 500 ormore island portions in one island-in-the-sea yarn, and production costscan be reduced, since several hundred microfibers can be produced fromone island-in-the-sea yarn.

FIG. 4 is a top view illustrating an upper plate of the spinneret forpreparing island-in-the-sea yarns according to one embodiment of thepresent invention. A spinneret for preparing island-in-the-sea yarns 200includes a discharge portion 210, through which island-in-the-sea yarnsare discharged, and a peripheral portion 220 surrounding the peripheryof the discharge portion 210. The discharge portion 210 has a structurein which a plurality of island ingredient supply channels 215 arepartitioned into groups based on four spinning cores 211, 212, 213 and214. The island ingredient supply channel groups are circular in thepresent invention, but are not limited thereto, and may have circular,oval or various non-circular shapes. The discharge portion 210 mayfurther comprise a sea ingredient supply channel 216. The position ofthe sea ingredient supply channel 216 is not limited. However, thearrangement of the sea ingredient supply channel 216 between adjacentisland ingredient supply channel groups is advantageous for preventingaggregation of island portions. Meanwhile, the number of the seaingredient supply channel 216 may be one or more. Like conventionalspinnerets for preparing island-in-the-sea yarns, the peripheral portion220 comprises sea ingredient supply channels 221, 222, 223 and 224, andthe number of the sea ingredient supply channels 221, 222, 223 and 224is not limited and may be equivalent to the number of the spinning cores211, 212, 213 and 214.

FIG. 5 is a longitudinal sectional view illustrating group-typeisland-in-the-sea yarns prepared using the spinneret of FIG. 4. Fourspinning cores are arranged in an island-in-the-sea yarn 250 and islandportions 255, 256, 257, 258 are grouped based on the spinning cores 251,252, 253 and 254. That is, a plurality of island portions 255, 256, 257,258 are partitioned based on the respective spinning cores 251, 252, 253and 254 and the island-in-the-sea yarn 250 has a cross-sectionalstructure in which as many island portion groups as spinning cores arepresent. In this case, the groups of island portions 255, 256, 257, 258arranged based on the spinning cores 251, 252, 253 and 254 may bedeformed, while edges of cross-sections are swollen, due to a dieswelling phenomenon during spinning of island-in-the-sea yarns, althoughthe island ingredient supply channel groups of the spinneret in FIG. 4have circular cross-sections. Accordingly, island portion groups of spunisland-in-the-sea yarns may have semicircular, sector, circular,spheroidal, polygonal or non-circular cross-sections, and their shapesare not particularly restricted and may be identical or different.Meanwhile, in the drawings, each spinning core is represented by a thickblack dot, which is shown for clearer description alone, and means onepoint acting as an actual center of the groups and the point may beeither an island portion or sea portion. Furthermore, spaces present inthe island-in-the-sea yarns may actually be filled with island portions,or only sea portions.

In a preferred first embodiment, one standard spinning core may bearranged in the center of the discharge portion 310 and a plurality ofperipheral spinning cores are arranged based on the standard spinningcore. Hereinafter, repeated description is omitted and onlydistinguishing characteristics of the first embodiment will bedescribed. FIG. 6 is a top view illustrating an upper plate of aspinneret for preparing island-in-the-sea yarns. Specifically, thedischarge portion 310 has a structure in which island ingredient supplychannels are grouped based on one standard spinning core 311 arranged inthe center thereof, and seven peripheral spinning cores 312, 313, 314,315, 316, 317, 318 are arranged outwardly based on the standard spinningcore 311. Sea ingredient supply channels 319, 320, 321, 322, 323, 324and 325 are interposed between the standard spinning core 311 andrespective peripheral spinning cores 312, 313, 314, 315, 316, 317 and318. Like conventional spinnerets for island-in-the-sea yarns, seaingredient supply channels 331, 332, 333, 334, 335, 336 and 337 may beformed in a peripheral portion 330 surrounding the periphery of thedischarge portion 310, but the present invention is not limited thereto.

FIG. 7 is an electron micrograph illustrating group-typeisland-in-the-sea yarns prepared using the spinneret of FIG. 6. As shownin FIG. 7, one standard spinning core 351 is arranged in the center ofthe island-in-the-sea yarn, and seven peripheral spinning cores 352 to358 are arranged based on the standard spinning core 351. In this case,preferably, the distances between the standard spinning core 351 and theplurality of peripheral spinning cores 352 to 358 may or may not besubstantially uniform. When the longitudinal cross-section of theisland-in-the-sea yarn is circular, aggregation of island portions isefficiently minimized if the distances between the standard spinningcore 351 and the plurality of peripheral spinning cores 352 to 358 aresubstantially uniform. On the other hand, when the longitudinalcross-section of the island-in-the-sea yarn is spheroidal, it ispreferred that the standard spinning core 351 and the peripheralspinning cores 352 to 358 be formed such that the distances between thestandard spinning core 351 and the peripheral spinning cores 352 to 358are long in a longer axis direction of the spheroid, but are short in ashort axis direction thereof.

Meanwhile, the number of peripheral spinning cores may be preferably 3to 20, more preferably, 6 to 10. As shown in FIG. 7, the mostadvantageous effects can be obtained when the number of peripheralspinning cores 352 to 358 arranged based on one standard spinning core351 is 6 to 8 and the number of grouped island portions in the standardspinning core 351 and peripheral spinning cores 352 to 358 is 100 to 200(Table 1).

In accordance with a preferred second embodiment of the presentinvention, the island-in-the-sea yarns comprise one or more spinningcores arranged based on the center of the discharge portion, and morepreferably, the island-in-the-sea yarns may comprise no spinning core inthe center thereof.

Hereinafter, repeated description is omitted and only distinguishingcharacteristics of the second embodiment will be described. FIG. 8 is atop view illustrating an upper plate of a spinneret for preparingisland-in-the-sea yarns according to the second embodiment.Specifically, a discharge portion 410 comprises three spinning cores411, 412, 413 arranged based on a center 430 thereof, and eight spinningcores 414, 415, 416, 417, 418, 419, 420, 421 are arranged outward of thespinning cores 411, 412, 413. At this time, both the three spinningcores 411, 412, 413 arranged at an inner region and the eight spinningcores 414, 415, 416, 417, 418, 419, 420, 421 arranged outward of thespinning cores are arranged based on the center 430 of theisland-in-the-sea yarn. In this case, the number of the spinning coresmay be 3 to 20, more preferably, 6 to 10, but the present invention isnot limited thereto. Meanwhile, a sea ingredient supply channel 430 maybe formed in the space between the spinning cores 411, 412 and 413, thatis, in the center of the discharge portion 410, and a plurality of seaingredient supply channels 422, 423, 424, 425, 426, 427, 428 and 429 maybe formed between the three spinning cores 411, 412, 413 and the eightspinning cores 414, 415, 416, 417, 418, 419, 420, 421. Furthermore, theperipheral portion 440 may also comprise a plurality of sea ingredientsupply channels 441, 442, 443, 444, 445, 446, 447 and 448. FIG. 9 is alongitudinal cross-sectional view illustrating the island-in-the-seayarn spun using the spinneret of FIG. 8. Specifically, three spinningcores 452, 453, 454 are arranged based on a center 451 of theisland-in-the-sea yarn, and eight spinning cores 455 to 462 are arrangedoutward of the spinning cores 452, 453, 454. At this time, both thethree spinning cores 452, 453, 454 arranged at an inner region and theeight spinning cores 455 to 462 arranged outward of the spinning coresare arranged based on the center 451 of the island-in-the-sea yarn.

Meanwhile, the number of island ingredient supply channels present inthe discharge portion may be 38 to 1,500, more preferably, 500 to 1,500and most preferably, 1,000 to 1,500, when the number of islandingredient supply channels is suitably controlled. Furthermore, thenumber of the island ingredient supply channels arranged in eachspinning core may be 10 to 300, more preferably, 100 to 150, althoughthe present invention is not limited thereto. Consequently, the numberof island ingredient supply channels arranged adjacent to each spinningcore may be suitably controlled under the conditions that the islandportions are not aggregated and fineness of island-in-the-sea yarns andisland portions, fineness of desired microfibers and optical modulationefficiency, as mentioned below, are maximized. Meanwhile, the islandingredient supply channels may have a diameter of 0.1 to 0.3 mm, the seaingredient supply channel may have a diameter of 0.1 to 0.3 mm. Theisland ingredient supply channel group may have a diameter of 8 to 15mm, and the discharge portion may have a diameter of 15 to 50 mm.Meanwhile, like conventional spinnerets, the spinneret has a funnel-likeshape wherein a lower plate, where island-in-the-sea yarns arepractically discharged, has a smaller diameter than the diameter of anupper plate. Like conventional cases, the discharge portion in the lowerplate may have a diameter of 0.1 to 0.6 mm. Meanwhile, the spinneret mayhave a maximum distance between the centers of adjacent islandingredient supply channels present in one group that is smaller than amaximum distance between the centers of adjacent island ingredientsupply channels in two adjacent groups. That is, the spinneret hasnon-uniform distances between two adjacent groups, thus making themaximum distance between the centers of adjacent island ingredientsupply channels forming the boundary between adjacent groups (themaximum distance between the centers of adjacent island ingredientsupply channels present in two adjacent groups) larger than the maximumdistance between the centers of adjacent island ingredient supplychannels present in one group. As a result, island ingredient supplychannels are not present in spaces between the groups and the spaces areempty, thus contributing to prevention of aggregation of island portionsin the center.

Furthermore, one spinneret may comprise 2 to 20 discharge portions andin this case, 2 to 20 threads of island-in-the-sea yarns can be obtainedthrough a single spinning operation.

The island-in-the-sea yarns prepared using the spinneret of the presentinvention will be sufficient, when they have a fineness comparable tosingle yarn fineness of common island-in-the-sea yarns and preferablyhave a single yarn fineness of 0.5 to 30 deniers. Of theisland-in-the-sea yarns, island portions preferably have a single yarnfineness of 0.0001 to 1.0 deniers, in view of efficient accomplishmentof objects of the present invention. Consequently, the group-typeisland-in-the-sea yarns enable arrangement of a maximum of islandportions and are thus considerably useful for mass-production ofmicrofibers.

Meanwhile, a luminance-enhanced film for LCDs can be fabricated usingthe island-in-the-sea yarns, whose sea portions are not eluted.

Conventional LCD devices do not necessarily have a high use efficiencyof light emitted from a backlight. This is because 50% or more of thelight emitted from the backlight is absorbed by a rear-side opticalfilm. Accordingly, in order to increase the use efficiency of thebacklight light in LCD devices, a luminance-enhanced film is interposedbetween an optical cavity and a liquid crystal assembly. However,conventional luminance-enhanced films are fabricated by alternatelystacking flat sheet-shaped isotropic optical layers and flatsheet-shaped anisotropic optical layers, which have different refractiveindices, and performing an extension process on the stacked structure sothat the stacked layer has an optical thickness and a refractive indexof the respective optical layers, which can be optimized for selectivereflection and transmission of incident polarized light. Accordingly,this fabrication process had a disadvantage of complicated fabricationof the luminance-enhanced film.

In particular, since each optical layer of the luminance-enhanced filmhas a flat sheet shape, P-polarized light and S-polarized light have tobe separated from each other in response to a wide range of incidentangles of the incident polarized light. Accordingly, this film has astructure, in which an excessively increased number of optical layersare stacked, thus disadvantageously involving exponential increase inproduction costs and deterioration in optical performance due to opticalloss.

Accordingly, the island-in-the-sea yarns prepared using the spinneret ofthe present invention are arranged to cause light emitted from a lightsource to be reflected, scattered and refracted on the birefringentinterface between the island-in-the-sea yarns and an isotropic sheet,thereby inducing optical modulation and considerably improvingluminance. Specifically, light emitted from an external light source maybe largely divided into S-polarized light and P-polarized light. In thecase in which only a specific polarity of light is required, theP-polarized light passes through a luminance-enhanced film without beinginfluenced by the birefringent interface. However, the S-polarized lightis modulated into randomly refracted, scattered or reflected wavelength,i.e., 5-polarized light or P-polarized light on the birefringentinterface. If the modulated light is reflected and irradiated on theluminance-enhanced film again, the P-polarized light passes through theluminance-enhanced film, and the S-polarized light is scattered orreflected again. Through repetition of this process, desired P-polarizedlight can be obtained.

Accordingly, when a plurality of group-type island-in-the-sea yarnsforming a birefringent interface with a sheet are arranged in the sheet,luminance can be considerably improved without using conventionalstack-type luminance-enhanced films. The present inventors found thatuse of general birefringent fibers as a polymer having birefringentinterfaces has an advantage of low production costs and easy production,but disadvantageously cannot improve luminance to a desired level and isthus unsuitable for industrial application, instead of the conventionalstack-type luminance-enhanced films.

Accordingly, the afore-mentioned problem can be solved by usingbirefringent island-in-the-sea yarns as birefringent fibers havingbirefringent interfaces. More specifically, the case where birefringentisland-in-the-sea yarns are used is found to provide considerablyimproved optical modulation efficiency and luminance, as compared to thecase where conventional birefringent fibers are used. Of the constituentcomponents of island-in-the-sea yarns, the island portions areanisotropic and sea portions partitioning the island portions areisotropic. This case, where the interfaces between a plurality of islandportions and a plurality of sea portions constituting theisland-in-the-sea yarns as well as the interfaces between theisland-in-the-sea yarns and the sheet are birefringent, exhibitsconsiderably improved optical modulation efficiency and is thusindustrially applicable as an alternative to stack-typeluminance-enhanced films, as compared to conventional birefringentfibers wherein only the interfaces between the sheet and birefringentfibers are birefringent. Accordingly, as compared to the case wherecommon birefringent fibers are used, the case where birefringentisland-in-the-sea yarns are used exhibits superior optical modulationefficiency and birefringent island-in-the-sea yarns which compriseisland portions and sea portions exhibiting different opticalproperties, thus enabling formation of birefringent interfaces therein,can more considerably improve optical modulation efficiency. Morespecifically, in island-in-the-sea yarns comprising optically isotropicsea portions and anisotropic island portions, the levels of substantialequality and in-equality between refractive indexes along spatial axesX, Y and Z affect scattering of polarized light. Generally, scatteringperformance varies in proportion to the square of the difference inrefractive index. Accordingly, as the difference in refractive indexaccording to a specific axis increases, light polarized according to theaxis is more strongly scattered. On the other hand, when the differencein refractive index according to a specific axis is low, a ray of lightpolarized according to the axis is weakly scattered. When the refractiveindex of sea portions at a specific axis is substantially equivalent tothe refractive index of island portions, incident light that ispolarized by an electric field parallel to this axis is not scattered,irrespective of the size, shape and density of a portion of theisland-in-the-sea yarns, but may pass through the island-in-the-seayarns. More specifically, FIG. 10 is a sectional view illustrating apassage in which light permeates birefringent island-in-the-sea yarns ofthe present invention. In this case, p waves (represented by lines) passthrough island-in-the-sea yarns, independent from the interface betweenthe outside and the birefringent island-in-the-sea yarns and theinterface between island portions and sea portions present inbirefringent island-in-the-sea yarns, while S waves (represented bydots) are affected by the interface between the sheet and thebirefringent island-in-the-sea yarns and/or the interface between islandportions and sea portions in the birefringent island-in-the-sea yarnsand are thus optically modulated. As a result, the group-typeisland-in-the-sea yarns render a specific color according to the ratioof sea portions to island portions and diameter of fibers, withoutadding chromogenic compounds such as dyes and are thus applicable tophotochromic fibers.

Meanwhile, it is preferred that the difference in refractive index intwo axes is 0.03 or less and the difference in refractive index in theremaining axis is 0.05 or more. In this case, P waves pass throughbirefringent interfaces of island-in-the-sea yarns, while S wavesundergo optical modulation. More preferably, when the difference inrefractive index between sea portions and island portions inisland-in-the-sea yarns in a longitudinal direction is 0.1 or more and,with respect to the remaining two axial directions, the refractive indexof the sea portion is substantially equivalent to that of the islandportion, optical modulation efficiency can be maximized.

Consequently, in order to maximize optical modulation efficiency ofisland-in-the-sea yarns, island portions and sea portions should exhibitdifferent optical properties and an optical-modulation area should bewider. For this purpose, the number of island portions should be aslarge as possible. However, conventional island-in-the-sea yarnscomprising 500 or more island portions have advantages of decreasedoptical-modulation interface area and deteriorated optical-modulationefficiency due to aggregation of island portions, although they compriseanisotropic island portions and isotropic sea portions. Accordingly, inthe present invention, aggregation of island portions can be solved bytwo or more spinning cores, although 500 or more island portions arepresent. As a result, the island-in-the-sea yarns prepared using thespinneret of the present invention exhibit maximized optical modulationefficiency and luminance-enhanced films into which the island-in-the-seayarns are incorporated also exhibit considerably improved opticalmodulation efficiency and luminance.

Any material for sea and/or island portions may be used so long as it iscommonly used as a material for island-in-the-sea yarns, and examples ofsea portions and/or island portions include polyethylene naphthalate(PEN), copolyethylene naphthalate (co-PEN), polyethylene terephthalate(PET), polycarbonate (PC), polycarbonate (PC) alloys, polystyrene (PS),heat-resistant polystyrene (PS), polymethylmethacrylate (PMMA),polybutylene terephthalate (PBT), polypropylene (PP), polyethylene (PE),acrylonitrile butadiene styrene (ABS), polyurethane (PU), polyimide(PI), poly vinyl chloride (PVC), styrene acrylonitrile (SAN) mixtures,ethylene vinyl acetate (EVA), polyamide (PA), polyacetal (POM), phenol,epoxy (EP), urea (UF), melanin (MF), non-saturated polyester (UP),silicon (Si), elastomers and cycloolefin polymers and combinationsthereof. In view of efficient improvement in optical modulation, it ispreferable to adopt materials for the island portions and the seaportions which have substantially identical refractive indexes in twoaxes, but have great difference in refractive index in one axis.However, it is more preferable that when polyethylene naphthalate (PEN)is used as a material for island portions in the birefringentisland-in-the-sea yarns and a copolyethylene naphthalate andpolycarbonate alloy alone or a combination thereof is used as a materialfor sea portions, luminance is greatly improved, as compared tobirefringent island-in-the-sea yarns made of common materials. Inparticular, when the polycarbonate alloy is used as the sea portions,birefringent island-in-the-sea yarns with the most excellent opticalmodulation property can be prepared. In this case, the polycarbonatealloy may be preferably composed of polycarbonate and modifiedpolycyclohexylenedimethylene terephthalate glycol (PCTG) and morepreferably, use of the polycarbonate alloy consisting of thepolycarbonate and modified polycyclohexylenedimethylene terephthalateglycol (PCTG) which are present in a weight ratio of 15:85 to 85:15 iseffective for improvement in luminance. When polycarbonate is present inan amount less than 15%, polymer viscosity required for spinningperformance is excessively increased and use of a spinning machine isdisadvantageously impossible, and when the polycarbonate is present inan amount exceeding 85%, a glass transition temperature increases andspinning tension increases, after discharge from a nozzle, thus makingit difficult to secure spinning performance.

Most preferably, use of the polycarbonate alloy consisting of thepolycarbonate and modified polycyclohexylenedimethylene terephthalateglycol (PCTG) which are present in a weight ratio of 4:6 to 6:4 iseffective for improvement in luminance. Furthermore, in view ofefficient improvement in optical modulation efficiency, it is preferableto adopt materials for the island portions and the sea portions whichhave substantially identical refractive indexes in two axes, but havegreat difference in refractive index in one axis.

Meanwhile, methods for modifying isotropic materials into birefringentmaterials are well-known in the art and for example, polymeric moleculesare oriented and materials thus become birefringent when they are drawnunder suitable temperature conditions.

Consequently, the island-in-the-sea yarns prepared using the spinneretfor preparing island-in-the-sea yarns of the present invention have astructure wherein island portions are partitioned into two or moregroups, and are thus free of aggregation of the island portions in thecenter thereof, although the number of island portions is 500 or more.Accordingly, island-in-the-sea yarns are considerably advantageous forthe preparation of microfibers, since 500 or more island portions can bedisposed in one island-in-the-sea yarn and fineness of island portionscan thus be reduced. In addition, the island-in-the-sea yarns have anadvantage of considerably reduced production costs, since 500 or moremicrofibers can be produced from one island-in-the-sea yarn.Furthermore, the island-in-the-sea yarns render a specific coloraccording to the ratio of sea portions to island portions and diameterof fibers, without adding chromogenic compounds such as dyes, and arethus applicable to photochromic fibers. When the island-in-the-seayarns, whose sea portions are not eluted, are applied toluminance-enhanced films for LCDs, they can impart maximumoptical-modulation effects thereto.

Hereinafter, the following Examples and Experimental Examples will beprovided for a further understanding of the invention. These examplesare for illustrative purposes only and are not intended to limit thescope of the present invention.

Example 1

An isotropic PC alloy (nx=1.57, ny=1.57, nz=1.57) consisting ofpolycarbonate and modified polycyclohexylenedimethylene terephthalateglycol (PCTG) in a ratio of 5:5 was used as a sea ingredient andanisotropic PEN (nx=1.88, ny=1.57, nz=1.57) was used as an islandingredient. In order to obtain island-in-the-sea yarns having thecross-section shown in FIG. 7, island-in-the-sea yarns (wherein 130island portions are arranged in one spinning core and a total number ofisland portions is 1040), were placed on a spinneret whose upper platehas the cross-section shown in FIG. 6. Under this composition, 150/24undrawn yarns were spun at a spinning temperature of 305° C. and at aspinning rate of 1,500 M/min and then drawn 3-fold to obtain 50/24 drawnyarns. FIG. 7 is an electron micrograph of island-in-the-sea yarns spunusing the spinneret of FIG. 6. As can be seen from FIG. 7, noaggregation of island portions was observed.

Comparative Example 1

The spinning was performed in the same manner as in Example 1 exceptthat the island-in-the-sea yarns were spun using a spinneret wherein onespinning core is present and 334 island ingredient supply channels arearranged in the one spinning core, as shown in FIG. 1. FIG. 2 is anelectron micrograph of island-in-the-sea yarns spun using the spinneretof FIG. 1. As can be seen from FIG. 2, aggregation of island portionswas observed in the center of island-in-the-sea yarns.

The spinneret for preparing island-in-the-sea yarns of the presentinvention exhibits superior optical modulation performance withoutcausing aggregation of island portions, and may thus be widely used forthe preparation of island-in-the-sea yarns applicable to microfiberfields, optical devices such as cameras, cellular phones and highluminance-requiring LCDs.

Although the preferred embodiments of the present invention have beendisclosed for illustrative purposes, those skilled in the art willappreciate that various modifications, additions and substitutions arepossible, without departing from the scope and spirit of the inventionas disclosed in the accompanying claims.

1. A spinneret for preparing island-in-the-sea yarns comprising: adischarge portion comprising a plurality of island ingredient supplychannels to discharge island-in-the-sea yarns; and a peripheral portionarranged in the periphery of the discharge portion, the peripheralportion comprising a sea ingredient supply channel, wherein the islandingredient supply channels are partitioned into a plurality of groups inthe discharge portion.
 2. The spinneret according to claim 1, whereinthe island ingredient supply channels are grouped based on two or morespinning cores.
 3. The spinneret according to claim 2, wherein thespinning cores include one standard spinning core arranged in the centerof the discharge portion and a plurality of peripheral spinning coresarranged based on the standard spinning core.
 4. The spinneret accordingto claim 3, wherein the peripheral spinning cores are 3 to 20 in number.5. The spinneret according to claim 3, wherein the peripheral spinningcores are 6 to 10 in number.
 6. The spinneret according to claim 3,wherein the number of island ingredient supply channels arranged withrespect to one standard spinning core or one peripheral spinning core is10 to
 300. 7. The spinneret according to claim 3, wherein the seaingredient supply channel is interposed between the standard spinningcore and the peripheral spinning core.
 8. The spinneret according toclaim 1, wherein the total number of the island ingredient supplychannels is 38 to 1,500.
 9. The spinneret according to claim 1, whereinthe total number of the island ingredient supply channels is 500 to1,500.
 10. The spinneret according to claim 1, wherein the total numberof the island ingredient supply channels is 1,000 to 1,500.
 11. Thespinneret according to claim 1, wherein the spinning cores are arrangedbased on the center of the discharge portion.
 12. The spinneretaccording to claim 11, wherein a sea ingredient supply channel isarranged in the center of the discharge portion.
 13. The spinneretaccording to claim 11, wherein the sea ingredient supply channel isarranged between the spinning cores.
 14. The spinneret according toclaim 11, wherein the discharge portion has a diameter of 15 to 50 mm,and the island ingredient supply channel or the sea ingredient supplychannel has a diameter of 0.1 to 0.3 mm.
 15. The spinneret according toclaim 1, wherein the island ingredient supply channel group has adiameter of 8 to 15 mm.
 16. The spinneret according to claim 1, whereinthe discharge portion is 2 to 20 in number.
 17. The spinneret accordingto claim 1, wherein the discharge portion further comprises one or moresea ingredient supply channels.
 18. The spinneret according to claim 1,wherein a maximum distance between the centers of adjacent islandingredient supply channels present in one group is smaller than amaximum distance between the centers of adjacent island ingredientsupply channels present in two adjacent groups.
 19. An island-in-the-seayarn spun using the spinneret according to claim 1.